The present invention relates to an optical disc cartridge construction having a mechanism for preventing incorrect insertion of the cartridge and, more particularly, to a 3.5" optical disc cartridge with such a mechanism.
There are currently three kinds of "write-once" type of optical discs on the market, namely 12", 8", 5.25". More recently, a 3.5" erasable optical disc has been under development. For designing a 3/5" erasable optical disc cartridge, a standard 3.5" magnetic floppy disc cartridge based on the U.S. "ANSI.times.3B8/86-57" proposal has been helpful. The structure of a 3.5" magnetic floppy disc is shown in U.S. Pat. No. 4,546,397. The diameter of a 3.5" magnetic floppy disc is 86 mm, the width of the cartridge is 90 mm, the length of the cartridge is 94 mm, and the cartridge thickness is 3.3 mm. The diameter of a 3.5" erasable optical disc is 86 mm, the cartridge width is 90 mm, the cartridge length is 94 mm and the cartridge thickness is 6 mm or 8 mm.
In a reproducing apparatus for a 3.5" floppy disc, accidental insertion of the 3.5" erasable optical disc cartridge can be prevented because the aperture opening of the reproducing apparatus for inserting the floppy disc cartridge is smaller than the thickness of the 3.5" erasable optical disc cartridge. However, in a reproducing apparatus for a 3.5" erasable optical disc, a 3.5" floppy disc which is thinner than its optical disc counterpart can accidentally be inserted into an aperture of the reproducing apparatus for the optical disc cartridge. In such a case, the optical head for retrieving data in the reproducing apparatus or a disc rotating portion can be damaged.